why is it that the earth and other planets in our solar system or all round andwhat makes them round????

Answer 1

They are travelling at a very high speed and spinning. Even though there is "no" atmosphere in space they are still subject to drag and friction. They have all had the "edges" knocked off them over a long (billions of years) time. If they weren't spinning they wouldn't be round!

Gravity isn't a complete answer. Why are the largest asteroids not round?

Answer 2

The shape of small objects (like people and houses and mountains and small asteroids) are determined by their mechanical properties. You can take a rock and cut it into a particular shape and it will pretty much stay that way.

The larger the object, though, the stronger its gravitational field. Imagine that you want to build a really tall building. You have to make sure it has a really strong foundation, or the foundation will be crushed by the weight of the building and the building will fall. If there was anything really big sticking up on a planet or a star, gravity would pull it down.

If a planet was like a cube, the corners of the cube would be higher than the rest of the planet. Since planets and stars are so big, you cannot build a "foundation" strong enough to hold up those corners! Anything you built it out of would be too weak to hold them up. Gravity would eventually pull them down.

Even solid rock will flow like a liquid, although very slowly, if it is pulled by a very strong gravitational force for a very long time. Corners on a cubical planet or star would eventually just squish down.

Since gravity pulls toward the center of the planet or star, everything gets pulled down into a sphere. However, planets and stars are not really perfect spheres. They spin, so they bulge out a little around the equator.

Answer 3

In short they're spherical due to any mass having a gravitational force. Therefore as matter gathers together, whether it liquid / gas / debris etc, they gradually become denser at the core and form a roughly spherical shape as a matter of course. It doesn't occur over night by a long shot.

And planets don't just form already orbiting suns, they are just rogue masses travelling through space until they themselves are caught in the gravitational field of a star and become stuck in orbit.

As for asteroids, as pointed out as not being generally round, is because they are usually debris from a larger, already formed mass and therefore cannot change shape... That and bits fall off / are collected during their travels.

Oh, and if bits did get eroded off into space we'd have no atmosphere first before the earth became spherical so no-one would be around to ask & answer questions....

Answer 4

Simplest answer is gravity.

The popular theory of planet building is called Accretion. This basically begins with a solar system full of gas and dust particles. The dust is remnants of earlier suns that have cast off material during the final explosive stage in the life of a star (called Novas or Supernovas).

Anyway, focussing on the planets, this debris is not evenly spaced and begins to form clumps because all objects in space attract all other objects (this is the Universal Law of Gravitation). The clumps attract each other forming larger and larger clumps.

As these collections of material get larger they attract bits of debris from further and further away, whats more they attract with a larger force (gravity depends on the mass of the object). So when the small bits of debris join the larger one they are travelling very fast, they have been accelerated. The energy of their impact is converted to heat and the original, growing, collection of debris starts to warm up.

This process of Accretion continues, as the mass grows bigger and bigger it attracts more and more debris all the time its temperature is rising. Eventually the ball of matter is glowing hot and melts into a ball of molten rock made from all the dust and particles it has collected. This process continues until most of the dust and debris has been sucked in and the solar system is relatively clear.

Now the rate at which new matter is added drops off and the ball slowly begins to loose heat and cool.

The shape of this molten ball will be spherical because gravity would pull any high points down into the mass.

The heavier materials will sink to the core(eg Iron), the lighter materials will sit on the surface(eg silicon). If the object has any rotation this will cause the molten ball to be slighly flattened at the poles and wider at the equator dues to centripetal forces.

Eventually a hard skin forms on the surface of the cooling ball and when the temperature is suitably low it may support life.

Answer 5

Why are these planets round? Well, every planet that actually existed has been round. It's because they spin around. Wouldn't it be kind of hard to spin if you were a rectangle or something like that. You'll bang into other planets all the time.

And it makes sense for a planet to be round even though they're irregular spheres.

Answer 6

The earth isn't completely round, its elliptical slightly and is squashed at the poles but i can't remember exactly by how much. However the normal state of any loose object is to form a sphere. This is the shape with the least surface area to mass, that's why bubbles are spheres. There is another shape with the same surface area to mass ratio but to my understanding it only exists in a computer model.

Answer 7

Short answer is gravity.
The sphere is the most economical shape, since all of the outer surface is more or less equal distance from the centre (centre of gravity). Liquid in space naturally forms itself into a sphere, as everyting has it's own gravity in the absence of a stronger field (like that of a star or planet)

Answer 8

a sphere is the shape with the smallest ratio between surface area and volume. liquids when not subjected to external forces tend to arrange the liquid volume in the form of a sphere, that is due to gravity, which pulls all material towards the mass center, since all planets are liquid as they form , the material arranges itself and later retains the spherical shape.

Answer 9

I know this probably sounds wrong since it is in space, but perhaps it is because of surface tension. Surface tension says that a liquid will form into a sphere (or close to it) when nothing obstructs it. This probably happened when the planets were still molten, billions of years ago.

Answer 10

Hmm, mabye it's like rolling dough into a ball. If you roll firmly it's quick, so mabye the air or energey or whatever is around us did that but took a long time, and now it's round. Also it's spinning so that might have had something to do with it.